1. Field of the Invention
The present invention relates to a storage system and a management method for a storage system.
2. Description of the Related Art
A storage system comprises at least one storage control device, called for example a disk array subsystem or similar, and provides data storage services to host computers (hereafter “hosts”). A storage control device can construct a storage area based on a RAID (Redundant Array of Independent Disks) system, in which numerous disk drives are arranged in an array.
As is known in so-called disaster recovery systems, it is possible to position a backup site remotely from the primary site in anticipation of widespread disasters and similar. A storage control device for backups is provided at the backup site, and the same data group as at the primary site is stored in the storage control device. By this means, even when the primary site operation is halted due to malfunctions or similar, data processing services can be continued by the backup site. However, if a malfunction occurs in the sole backup site, data processing services cannot be provided to hosts.
Hence technology has been proposed to provide a plurality of backup sites, so that even if operation of the primary site halts, the system redundancy is retained (Japanese Patent Laid-open No. 2005-84953). In the prior art disclosed in this reference, as described in paragraphs numbered 0008 to 0010, a plurality of secondary storage control devices are connected to the primary storage control device. When the stored contents of the primary storage control device are updated, the updated contents are immediately transmitted to one of the secondary storage control devices, and are reflected in the stored contents of the one secondary storage control device. The stored contents of the primary storage control device are saved as journal data, and other secondary storage control devices read this journal data as appropriate and reflect the data in their own stored contents. The one secondary storage control device creates journal data based on a data update command from the primary storage control device, and saves the journal data. When operation of the primary storage control device stops, the other secondary storage control devices read the journal data from the one secondary storage control device, and update their own stored contents.
In another technology of the prior art, the storage contents of the first storage device of a primary site and the storage contents of the third storage device of a local site are kept in permanent synchronization through remote copying, while the storage contents of the first storage device and the storage contents of the second device of a remote site are made to coincide periodically (Japanese Patent Laid-open No. 2005-78453). When a disaster befalls the primary site, only the differential data between the storage contents of the first storage device and the storage contents of the second storage device are remotely copied from the third storage device to the second storage device.
In the technology disclosed in the first and second references, when operation of the primary storage control device is stopped, redundancy can be retained through the plurality of storage control devices, and the reliability of the storage system can be improved. However, in the first reference, the one secondary storage control device must generate journal data each time data updating is performed, so that the load on the one secondary storage control device is increased. Moreover, a volume must be provided to save the journal data in the one secondary storage control device, so that there is the problem of increased structural complexity.
In the technology described in the second reference, a copy volume of the primary volume in the first storage device is created, and the storage contents of this copied volume are made to coincide with the storage contents of a volume in the second storage device. Hence volume copy processing and similar is necessary, and the period during which the storage contents of the first storage device and the storage contents of the second storage device are not coincident becomes comparatively long. Further, it is necessary to prepare in advance a volume for copying with the same capacity as the primary volume.